Ahh...I see a younger me in you now that I'm reading your story *lol* And like what others said, you'll have to prioritize between what's important to you at the moment.
Some jobs you can push your luck while others can't. It depends on whether you wanna take the risk or not.
Share with you my own story. I'm now working in NUS as an admin and in this almost 'front-line' and educational industry, I'm supposed to look decent and all and portray a good image. And like you, I'm a long-hair-favouring guy and when I first worked here, I adhered to the rules and cut my hair short. But as time goes by, I grew my hair long again, did lots of whacky, radical styles (bleaching it half-blonde or dye it red, etc) and none of my colleagues/bosses/supervisors complained about it. I think the key thing is your attitude, character and good working mentality/ethics, etc. If you've proven to them that you're a person of integrity, work well, polite, and all, they'd have an easier time accepting it. Of course, a big part of it depends on your higher authorities if they can bend the rules. I'm damn lucky to have a good boss and colleagues who don't mind these things.
If you think your life will be a much more enriching experience with this 'rock and roll long hair care free' type of lifestyle, then go for it. For some, having a job is a responsiblity and can't afford to do such stuff. Again, I'm lucky to have both sides of it taken care of
Good luck!
P.s Having said that, I still dread the reservist period...cannot siam wan lah. But luckily, hair can still grow